Method and apparatus for handling acidic solutions



2 Sheets-Sheet l R. m 0 V I I I I I I I I I. I v I I I I I\ Paul L.Men8ul. BY w w f' ATTORNEY P. L. MENAUL METHOD AND APPARATUS FOR HANDLING ACIDIC SOLUTIONS Filed Dec. 19, 1936 March 7, 1939. p, MENAUL 2,1495617 METHOD AND APPARATUS FOR HANDLING'AIDIC SOLUTIONSv w Filed Deo. 19, 1938 2 sneets-'sheex 2 IN VEN TOR.

Pau! L. Nenaul.

BY 'wf/5M,

A TTORNEY Patent'ed Mar. 7, 1939 METHOD AND APPARATUS FOR. HANDLING ACIDIC SOLUTIONS V Paul L. Menaul, Duncan, Okla., assignor to Halliburton Oil Well Cementing Company, Duncan,

Okla.

Application December 19, 1936, Serial No. 116,768

ucizims.

This invention relates to method and apparatus for handling acidic solutions, and more particularly to electro-chemical means and method for protecting metals against corrosion caused by exposure of the metals to strong acids.

This application is in continuaticn in part of the copending application of Paul L. Menaul, Serial No. 77,945, filed May 5, 1936, for Method and apparatus for handling acidic solutions."

l" Strong solutions of hydrochloric acid and other acids attack various metals, and the present invention is intended to protect metals, particularly iron, from the corrosive action of such acids.

It is known to the art to protect metals from '5 weak acids by electrical means, but the methods heretofore employed for this purpose are generally ineifective in protecting metals from strong acids.

It is one object of the present invention to pro- 20 tect iron and other metals from strong acids by electro-chemical means and methods which will eifectively pacify them with respect to the acid without impairing the normal properties of the acid to any material extent.

A further object of the invention is to provide means and methods of acid-treating oil wells or the like whereby corrosion of metallic equipment, such as casing or tubing, in co`ntact with the acid or acid solution is retarded.

' Other objects and advantages reside in certain novel features of the arrangement and method, as will be apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a diagram illustrating an iron and a lead electrode in a beaker of hydrochloric acid,

lthe arrangement illustrating some principles 'of the invention.

Pig. 2 is a diagram similar to Flg. 1, but illus- 40 trating a slightly different arrangement.

Fig. 3 is a diagrammatic Illustration, in vertical cross-sectional view, of an oil well and illustrating one embodiment of the invention applied thereto to protect the metal therein.

Fig. 4 is a diagrammatic illustratlon of a modifled form of the invention as applied to an oil well.

Flg. 5 is a Vertical cross-sectional view of a container for acid constructed in accordance with the invention.

lFig. 6 is a diagrammatic illustration of the upper portion of an oil well, together with a tank constructed in accordance with the present invention for Supplying acid to the well and a pump for forcing the acid from the tank into the well; 56 and Fig. 7 is a diagrammatic illustration of a tank and well similar to that of Fig. 6, but illustrating a modified arrangement.

In describing the invention, some underlyins principles will first be explained and this will be 5 followed by a disclosure of some adaptations of these principles to oil well equipment to which they are particularly applicable.

When two electrodes of different metals are immersed in an electrolyte, a difference in electrical potential is created between them and current tends' to fiow from one to the other through the electrolyte.

The difference in potential and the direction of fiow of current depends upon the nature of the electrodes selected and possibily in some cases on the nature and condition of the electrolyte.

Metals may be arranged in what is called a voltaic series or electro-chemical series, the position of any given metal in the series being determined by the direction of fiow of current through the electrolyte from that metal to any other in the series, when terminals on the electrodes are connected by an electrical conductor exterior to the electrolyte.

The current fiows through the electrolyte from what is herein termed the more electro-positive plate or element to the other, and then back to the electro-positive plate or element through the external conductor.

In a galvanic cell like that shown in Fig. 1, having iron as one electrode and commercial sheet lead as the other electrode, with hydrochloric acid as the electrolyteI the lead electrode is electro-positive with respect to the iron electrode.

The iron becomes the positive pole of the cell and extemally the current flows from the terminal of the iron electrode to the terminal of the lead electrode. The voltage causing this current is very low, being only about 100 millivolts.

This voltage is in the proper direction to tend to protectthe iron against corrosion, since the current is fiowing from the acid to the iron, but because this force is very small, it is ineifective for this purpose and, for a time, corrosion of the iron takes place. i

However, this corrosion does not continue. The corrosion of the iron by the hydrochloric acid' soon diminishes to a negligible amount. The explanation for this phenomenon must be found elsewhere than on the basis of a mere difference in electrical potential, it being known that such small voltages are not capable of producing the desired result. i i

Now, it is known that lead may be deposited on iron by causing an electric current to pass through hydrochloric acid in which the lead has been dissolved, and the most obvious explanation for the above described phenomenon is that some lead has gone into solution in the acid and become deposited on the iron, thus forming a protective coating or-lead plate on the iron.

An examination of the iron electrode after a time shows this to be a fact. There is a visible but immeasurably small deposit of lead thereon. But if this electrode is now placed back into the acid with the lead electrode removed, after a time corrosion starts up again and once it starts it continues at a more rapid pace than ever, both the lead and the iron going into solution in the acid. This minute deposition of lead on the iron may have something to do with the preventionl of corrosion, but it seems clear that other than electroplating factors are involved and that the extremely small amount of lead deposited is ineffective per se, to obtain the desired result.

It is thus seen that in the cell mentioned, the voltage or the difference in potential is insufiicient to obtain protection and that the extremely small deposition of lead on the iron is insufilcient to form a protective insulating coating.

The results obtained, therefore, must be due to the combination of difference in potential and the electroplating of lead on the iron. This leads to consideration of what is called hydrogen overvoltages, a discussion of which is'believed to be necessary in order to understand not only the basic underlying principles of the behavior of iron and lead in the example given above but also the broader adaptations of the invention to metals and electrolytes other than those mentioned herein.

It is known that when an electrode is placed in an acid, and current is passed from the acid to the electrode, hydrogen is disassociated from the acid and passes of! as bubbles. There ,is little or no bubbling ofl of the hydrogen however until the certain critical voltage between the acid and the metal is reached. This critical voltage is called the decomposition voltage" of the electrolyte.

It is further known that the decomposition voltage" varies, depending on the nature of the electrodes. The difference between the actual potential at which there is visible evolution of hydrogen gas with a certain metal as electrode and the potential at which decomposition starts in the same solution with a hydrogen electrode, is called the hydrogen over-voltage of that metal.

Now, lead has a much greater hydrogen overvoltage" than iron in hydrochloric acid, and it is believed that the very slight deposition of lead on the iron in the example given above, while ineffective to isolate the iron completely from the acid, is effective to increase the hydrogen overvoltage of the iron electrode. The iron cannot go into the solution in the acid unless hydrogen molecules are liberated, and the abnormal hydrogen over-voltage prevailing on the iron electrode, due to the lead thereon, coupled with the small difference in potential resulting from galvanic action, prevents this taking place. This is believed to be the theory underlying the peculiar behavior of iron and lead in the example given and it is thought that the same principles may be applied to other metals.

If desired, the normal difference in potential between the plates of the cell of Fig. l may be altered (preferably increased) by an external battery. Such an arrangement is shown in Fig. 2. The operation of this arrangement is the same as that in Fig. l except that the'voltage between the plates may be altered to best luit the conditions.

As mentioned above, commercial Sheet lead was used as the anode in the galvanic cells described above to illustrate the above principles.

Commercial sheet lead was selected because it appears that with iron and with hydrochloric acid, the galvanic cell thus constructed has just the right voltage to give the desired protection without any considerable amount of the lead going into the solution.

One peculiarity in the behavior of iron which has been used for some time as an electrode in a cell like that described is that it has become temporarily pacified. After the thin fllm of lead has been deposited thereon for some time, the lead electrode may be removed and so long as the iron electrode is not disturbed, the acid will remain inactive with respect to it for quite some time. This is probably due to the adsorption of hydrogen by the lead film from the acid.

On the accompanying drawings, several adaptations of the above princip'les to oil well equipment are shown.

Referring to Figs. 3 to 7 of the drawings in detail, and first to the arrangement of Fig. 3, the well hole indicated at i contains a casing indicated at 2 which terminates at the top of an oil-bearing strata 3. In accordance with customary practice, the casing is shown cemented in the hole, the cement being indicated at 4. Extending downwardly through the casing is a well pipe 5 which extends beyond the casing into the well bore puncturing the'formation I. The well pipe 5 may carry a packer 8 blocking the upward passage of iiuid through the annular space between the well pipe 5 and the casing 2. The casing head and other devices commonly found at the top of a well hole are not shown.

In acid treating the formation 3 for the purpose of increasing its porosity or removing obstructing matter which restricts flow of oil into the well hole, an acidified solution such as, for example, a 15% hydrochloric acid solution, is pumped downwardly through the pipe 5 into the formation. In practice, the solution is pumped into the formation for an appreciable period of time of, say, from several hours to several days. Since the acid is in contact with the casing or tubing or both while being placed in the well, it may corrode the same. In accordance with this invention, however, a metallic member such as a cable or wire is let down through the pipe 5, such wire being indicated at 1.

The wire or member 'I is preferably of a metal which is electro-positive to the metal of the well pipe 5. For example, since most well pipes are of iron, the wire 1 may be formed of commercial lead, a lead alloy, or it may be lead sheathed cable which externally of the electrolyte has been found to have a more negative potential than iron in hydrochloric acid. The lower end of the wire may bc provided with a large weight, such as the lead weight 8. A metallic electrical conductor, such as a copper Wire, is'then attached to the metallic member or Wire 'l and to the well tubing or pipe 5 at or near the top of the tubing. Such electrical conductor is indicated at 9.

It will be noted that the wire 'l is immersed I anaei' mnie acid' science mdleated' at' lo. sii'h acid;

solution contacting |.not only theV wire 'l but also battery is. formeaby the elements descnbed and the electrodes become polarized, .which decreases v and ineffect prevents the acid from 'corroding thepipe. As explained above in connection withiFlg. 2, in certain cases it has been found 'desirable' ;to

apply -an additional potential tofplates of the cell, such potential being in the same direction or polarity as the electromotive force which is attainedr by the use of the pipe, electrode and acidic solution alone. For this reason the positive pole of a battery or applied electromotive force may be connected to the lead electrode in the well, whichV is in the acid solution, and the negative pole of the battery or applied potential may be connected to the iron casing or the metal which is to be protected. As indicated in Fig. 4, for example, the external circuit 9 may include a battery or other source of electrical energy. lThe precise voltage or amperage .of this source need not necessarily be fixed or critical. It has been found, for example, that by using l or 2 cells of a storage battery furnishing approximately 2 or 4 volts is sumcient to give the deslred polarization and obviate corrosion.

As a matter of fact, when'a sufiiciently large potential is applied in the external circuit 9, such a` potential being superimposed on the E. M. F. normally obtained by the pipe, electrode and acidic solution, an electrolytic action may-take place whereby migration of considerable lead from the electrode 1. to the interior walls of the pipe 5 is attained. This electrodeposition of lead upon the interior surfaces is usually exceedingly minute but does form a protective coating thereon, but excessive external voltage should not be applied. At about 4% volts, for example, a spongy lead deposit may be formed on the interior of the tubing, which spongy lead does not adhere with yany great tenacity and oftenfalls oif when itis disturbed.

The electrode cable 'I may be introducedinto thewell either prior 'to the introduction of acid solution `or immediatelythereafter. The cable should be of. sufficlent weight and of a suflicientlylarge size so that in the event any electrolytic action does take place, it does not completely disintegratebefore the termination of the acid treatment.

. l'I'he method of this invention may alsobe appliedto the treatment of tanks or other conltainers in which acid is stored or shipped. A suit- 'connected to the iron-or steel tank, either with or without-the medium .of a battery or other source of low voltage direct-current. Aszshown in Fig.,5,,'for example,'-the iron tank` I'Zmay have a' leadu plate '13' .in electrical ,contactV with the bottom of vthe-container.L .Such-contact may be so that the acid fco'ntained therein may contact with both the lead and the sheet iron. Desired polarization of the interior of the tank is thus attained.

i' A 'particularly effectiya'wayof 'protectin'g 'both thetank used `in conveyin'g the acid tov the'welll andalso the casing, tubing "oz-'other metal parts of .the well is shown inFig; 6. Thi s was disclosed to 'some extent'in'gclaim'aof the' copending application referred to above;` f

` In Fig. 6 an iron tank for conveying the acid is illustratedat lHI. `'I'hejtanl'r'may `be mounted on a' truck or trailer :and `obviously may 'be of any' desiredsha "j A lead vplate |5 is burned or otherwise'secured to the tank H so as to provide at least one pointV whlre it forms'a good electrical connection there- The galvanic cell set up by'the lead plate and the iron tank vwhen, strong hydrochloric'acid is placed therein'eifectiv'ely protects the tank, 'as explained above in connection with Fig. 3.

.Upon arriving at the oilwellinto which the acid is to be pumped,j an electrical conductor or cable |6 is connected' between the tank ll and the casing or tubing l'l f the well. The conductor IS may be permanently welded to the tank as shown at |8 and may be clamped to the casing asv shown at |9. Any otherway of effecting good electrical contact will serve the purpose'.

If now a pump, such as that diagrammatically shown at 20, is operated to cause the acid in the tank to fiow through the acid conduits 2| and 22 in the' well, an electric circult will be set up and current will fiow fromthe acid in the well to the casing l'l; the electrical conductor vIS, the tank H and the lead plate |5 back to the acid.

The effect is the same as though the casing l'l became part of the tank |4, and corrosion of the casing l'l will not take place, even though it is several thousand feet in length.

It is remarkable to note that casing many thousand feet from the lead plate |5 is pacified. The

`vvise cause a high 'resistance to develop. This -would increase the current density adjacent other parts of the 'w`ell.' A film would tend 'to form wherever it did not alreadyexist and once formed would tend to cause the current to flow from the .acid to the casing Somewhere else'which in turn wouldtend to cause the formationof a film there.

and solion, every. part of the casingi being protected as soon as that part is, contacte'd byv'the acid.

It may be'desirable in some instances to supplement. the voltage generated .by the 'galvanic' o action in the. tank of Fig'. l'6 byfanv auxiliary source of direct current potential and an arrangement for accomplishingthis is showninFig. 7.

v The ;system'in Flg. "l isthesameas that in F181. 6, except that a storagebattery or .the like has been connected into the conductor JS, as shownat 23. This batterymustbe so connected as to cause current to A,iioiivmfrom thecasing l'l to the tank Il, sincethis is thev directlonof fiow caused bythe-. galvanioaction inthe tank.v`

Whether an auxiliary source Vof-,potential lis employed .or not, the conductor ,IS may be connected to the tank almost anywhere, but it could equally well be connected to the plate IS directly. The electrical resistance of the tank beingA low,

the point of connection of the conductor ll thereto does not make much difference.v

Another peculiarity of the invention is that it does not make much difference what kind of material is used for the acid conduits 2| and 22. If these conduits are of iron they are connected to the tank through the casing i'l and conductor IS and-are readily pacified. If rubber or canvas hose is used it makes no difference because a path for the flow of current is provided by the acid itself from the acid in the tank to the acid in the well. i

When an auxiliary source of potential is used, as shown at 23, in Fig. 7, the voltage must not be too high, preferably not over 4 to 6 volts, or considerable lead will go into the solution and be deposited on the iron. This does not do any harm, other than being wasteful, but neither does it do much good in protecting the casing or tank. It would be practically impossible to lead-coat the entire casing and the protection can be just about as effective with only a trace of lead being in the solution.

On the other hand, unless some lead does go into solution, what protection there is is wholly insufficient. A high direct current potential connected as illustrated in Fig. 7, lin the absence of any lead in the tank H, would not accomplish the purpose of the present invention.

In the following claims, where hydrochloric acid" is recited, various solution concentrations are intended to be included; where "iron is recited, various alloys of iron or steel are intended to be included; and where "lead is recited, various alloys in which lead is the principle ingredient are intended to included.

It will thus be clear that although only a few embodiments of the invention are shown and'described herein, the principles are ,of broad application and that many changes may be made, both in the structure and method, without departing from the spirit of the invention or the scope of the annexed claims.

I claim:

1. A method of acid treating wells which includes introducing hydrochloric acid into the well hole and into contact with -the earth structure to be treated through and-in contact with an iron well pipe, introducing` a tlead electrode into the well pipe and into contact with the acid and electrically connecting said pipe and electrode. e

2. A method of acid treating wells which includes introducing hydrochloric acid into the' well bore and into the earth structure to be treated through an iron well. pipe, introducing a lead electrode into the well pipe and into contact with the' acid, and applying a direct current potential to the electrode and pipe, the negative pole of the applied source of current: being connected to the well pipe and the. positive pole being connected to Ithe aforesaid electrode in acidic solution.

3. A method of acid treating wells which includes introducing hydrochloric acid from an iron tank into a well bore and into contact with the earth structure -to be treated through an iron well pipe; electrically connecting a lead electrode to said tank, the electrode being in contact with the acid but not covering all of the -tank in contact with the acid, and electrically 'connecting the tank to the well pipe.

4. A method of protecting from corrosion'an and to the iron bodies.

iron vessel containing hydrochloric acid in contact with said vessel which includes electrically connecting a lead electrode to the vessel, said electrodebeing in contact with the acid therein.

5. The method' of protecting from corrosion, a. body of iron exposed .'to and ,in contact with hydrochloric acid which' includes placing a lead electrode in the acid and electrically connecting the electrode to the body of iron.-

6. Apparatus for acidizing an oil well and for protecting the iron equipment thereof during the placing of hydrochloric acid therein which includes, in combination with the iron equipment of the well, an iron tank adapted to hold the acid, an electrode of lead in the tank and so positioned as to contact the acid, means for electrically connecting the -tank to the iron equipment, and conduit means for conveying the acid from the tank into the well, said conduit means being so arranged as to provide an electrical connection from the acid in the tank |to the acid in the well through the acid in' said conduit means when the acid is flowing therethrough.

'7. Apparatus for acidizing oil wells with hydro- I ohloric acid which includes an iron pipe in the well, an iron tank adapted to contain the acid to be supplied to the well, said tank having a plate of lead electrically connected thereto in contact with the acid therein, a pump for pumping the acid from lthe tank into the well, acid conduits connecting the tank to the pump and the pump to the well, and means for electrically connecting the tank to the pipe in the well.

8. The method of protecting iron in contact with hydrochloric acid from corrosion due to that contact which includes dissolving a trace of lead Vin the acid, electrically depositing a film of the 'the acid to cause a trace of the lead to be dissolv'ed in the acid, electrically depositing some of the lead so' dissolved on the iron to form a protective coating thereon and impressing a low` voltage of direct current between the acid and the iron to maintain said coating.

10. The method of protecting iron in contact with hydrochloric acid from corrosion due to that contact which includes placing a body of lead in the acid to cause a'trace of the lead to be dissolved in the acid, electrically depositing some of the lead so dissolved on the iron to form a protective coating thereon and impressing a low voltage of direct current between the acid and the iron -to maintain said coating, said voltage being maintained by causing galvanic action in the acid by electrically connecting the lead to the iron.

ll. The method of increa'sing the output of a petroleum well by treating a petroleum baring formation with acid, while protecting iron bodies 'in the well which includes the steps of connecting a conduit to the well and to a tank containing the acid, causing the acid to flow from the tank into the well and electrically pacifying the acid with respect to' lthe iron bodies in the well by placing a lead electrode in the acid in the tank and electrically connecting the electrode to the tank PAUL L. MENUL. 

